1. Field of the Invention
This invention relates to a laminate type piezoelectric device used as a driving source of an injector.
2. Description of the Related Art
An injector (fuel injection device) of an internal combustion engine of an automobile, or the like, is constituted in such a fashion that when a valve body of a three-way valve or two-way valve connected to a common rail storing a high-pressure fuel is operated, an open/close state of a fuel passage is changed over to thereby change a pressure condition applied to a nozzle needle, and the nozzle needle is brought into an open state so as to inject fuel.
A solenoid valve has been used ordinarily as a driving source for operating the valve body. Attempts have been made to employ a laminate type piezoelectric device as the driving source so as to finely control the driving source and to precisely control the fuel injection state as described, for example, in Japanese Unexamined Patent Publication (Kokai) No. 11-229993.
However, an injector using the piezoelectric device for the driving source has not yet been put into practical application though proposals have been made as described above.
In the injector, atomization of the fuel must be repeated at an extremely high speed. In cases, atomization is done more than 10,000 times per minute. Therefore, extremely severe conditions are imposed on the piezoelectric device as the driving source when it is used in practice. No piezoelectric device has yet been developed that can be sufficiently used under such severe conditions without inviting cracks, and so forth.
A practical injector must have not only a sufficient driving force but must be small enough to be accommodated in a small accommodation space.
Further, to accommodate the piezoelectric device in the injector, it is effective to accommodate the piezoelectric device into a cylindrical case. When accommodated in this cylindrical space, the piezoelectric device must exhibit excellent dynamic performance (large force generation). When the piezoelectric device is accommodated in the cylindrical accommodation space, the temperature rise resulting from self-exothermy of the piezoelectric device becomes a problem. Therefore, heat radiation performance must also be improved.